A single layer of epithelial cells separates the intestinal lumen from the host's internal milieu. Clinically relevant foodborne pathogens may reside in the intestinal lumen in close contact with epithelial cells, adapt an intraepithelial cell lifestyle, or invade the epithelium as well as deeper layers of the intestinal mucosa and spread systemically. Despite these markedly different microbial lifestyles, and various mechanisms for causing host disease, a common feature of foodborne pathogens is their interaction with the host intestinal epithelium. Therefore understanding host intestinal epithelial cell responses to foodborne pathogens is central to the development of strategies to alter the host-pathogen interaction to the advantage of the host. The overall long-term goal of our studies is to define the repertoire and functional relevance of intestinal epithelial cell responses to foodborne pathogens. We hypothesize that intestinal epithelial cells express a relatively narrow repertoire of responses that are relevant to host innate and acquired immune defense following infection with foodborne pathogens. The proposed studies focus on three types of intestinal epithelial responses to foodborne pathogens that we consider will be particularly important for host innate and acquired defense. The three specific aims of the proposal are 1) to characterize the regulated expression and possible autocrine/paracrine function of intestinal epithelial cell expressed MIP-3alpha in the host response to foodborne pathogens; 2) To define epithelial cell apoptosis as an important host response to infection with foodborne pathogens; and 3) To define the regulated expression of antimicrobial peptides by human intestinal epithelial cells in response to epithelial cell infection with foodborne pathogens. These studies will use Salmonella as a model of an enteroinvasive foodborne pathogen, Cryptosporidium parvum as a model intraepithelial pathogen, and Escherichia coli O157:H7 as an intraluminal pathogen that lives in intimate association with the apical intestinal epithelial cell membrane. Our experimental approaches will draw on in vitro and in vivo model systems established in this laboratory and a duality of hypothesis and discovery based experimental approaches.